Traveling wave tube



Oct. 27, 1953 R. L. WATHEN 2,657,329

TRAVELING WAVE TUBE Filed Feb. 21, 1950 3 Sheets-Sheet l INVENTORRo/SWL. Wem/5N @ai m' ATTORNEY focr. 27, 1953 R. L. WATHENr 2,657,329

TRAVELING WAVE TUBE Filed Feb. 21, 1950 svsneets-sneet 2 |||||m,A@05E/UL. MME/V A 70' @y 6M ATTORNEY INVENTOR Oct. 27, 1953 R. l..wA'rHEN 2,657,329

TRAVELING WAVE TUBE Filed Feb. 21, 195o s sheets-sheet s Fig.

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INVENTOR ROBERT Wan/w ATTORNEY Patented Oct. 27, 1953 UNITED STATES;

PATENT OFFICE' Application -February-21, 195ll-SeriaLNo.,145,360.

4 Claims; 1

This. invention. relates. to improvements in travelling wave tubes and.more particularly to.. travelling waveY tubes. ofthe distributedklystron type., wherein a sheet. like. stream of electrons.v flowsitransversely to, the. direction of, wavev propagation, across one or.more. electron permeable.v wave guides, interacting with the. waves..travelling thereinto produce amplification. One such type of. travellingwave tube, involving two wave guides used as. input. and output means.or buncher andfcatcherf"respectively, is described.. incopendin-g U.. S.patent application Serial No. 86`,018.led April` 'lJv 1949 by Edward L.Ginzton. and entitled. Electrony Discharge. Devices.

One of the principal, objects of the present in.- vention. is to.provide travelling. wavetubes of. the general type describedl in said.-copending. applica'- tionb,ut including one. or more wave guides in-vtermediate. the buncher and catcher to. provide. cascade.v operation..

Another object'is-to provide improved.. oscillav tor systems including.travelling wave tube struc-.- tures of, the above mentioned type..

A more specic object is to provide travelling/1 wave; tubei oscillatorsincluding. one or more buffer stages serving. to isolate. the. outputmeans from the oscillation-generator means.

A tur-ther object. is to provide.. cascade. travel-.- ling wavetubes invwhich. different sections of' a single guideor wave trans-mission.conduit. react. withan. electron stream,l the intermediatesectionstoithe. guide acting as.. catchers withy respect toy the.preceding sections and as. bunchers withvr respect.- to the succeedingsections..

Itis another object oi this inventionto provide improved., travelling,wave tubes which may be designedv compactly and. are. capable ofrelatively high. amplification `and/or large power output with. a .giventotal, beam current. and dissipation.

The. invention will. be described with reference tothe accompanyingdrawings,A wherein:

Fig. l5. an elevation insecti'on of a cascade amplifier tube embodyingthe invention,

Fig, Z is. a transverse cross section of one of; the wave guides in thevdevice of Fig; 1,

Figs. 3',A 4' andy 5 are sections' of the` structure` off l in theplanes o 31"--3'y 4-4', and 5-5 respectively of Fig. 1,.

Fig. Sis a perspective view of a mod-inedoscilator-buier amplifierincorporatingl substantially 5o the same principles as the tube of;Fig'. 1 but of different construction, e

Fig. '7 is an elevation,I partly-in section off' a mod'ied cascadeampliertube;

Fig. 8` is an elevation, partly in section, of4 a 55 further modicationof the structure of Fig; 7',

and

2; Fig. 9 isa section or the structure of Fig. 8. inthe/plane 9-9 of'Fg.81

The cascade amplifier represented in Fig. I

includes three wave guides l, 3 and supportedl in spacedparall'elrelationship by the wallsofa vacuum-tight enclosure or envelope l',which may be of metal. The waver guides may be of.l reentrant crosssection; as shownr in Fig. 2. A part. of the waveV guide! within. theenvelope 1 is provided with a longitudinally. extending slotV 9 in.

its upper wall and a similar. slot H in. its reentrant Wall. Theseslotsimaybe; taperednear theirv ends 20' and.2"0 as shown bythe planview of the slotu ll in Fig. 3. The` Wave guides and 5. are providedwith similar slots 9,.. |.I" and; 9; II" respectively..A

A cathode assembly I3' issupported near and below the lower wallof.thewave guide 5 on posts,

IF which extend through and are supported by vacuum tight insulatingbushings or seals I1. in the` bottom of; the envelope. T. The.. cathode,asf sembly includes a heater element i9 connected' between one ofl the.posts |5A and a similar in-v sulated post 21. The reentrant. portion atthe bottom of .thewave guide 5' is covered by a conductive sheet' orplatezwhichmay be flush with the. bottom wall as shown', and is providedwith a longitudinal slot Z5 likethe slots 9 and I'I..

A collector electrode in the form ofA a.,relatively long narrow metalstripA 21 is supported on in:- sulatedposts 2,& above the slot 9 in theupper wall offthe` waveI guide l. The slots 9, I'l,9, I.l.,y etc. in thewave guides may be provided with electron permeable grid structures, ormay,l be gridless as shown.. in Figs. 3, 4 and 5L, dependingupon theamount of; power that is to` be handled by4 the tube.

The lefthand end, of' the wave guide l is closedV byl a wall 29; and`the reentrantY portion of? the waveguide I near this end is replaced byva bodyl 3I` oitnlagneticstainless steel, or similar lossy materialsuitablel for' use in vacuum. The body 3l acts asa terminatinglimpedance to minimizey reflection of wave energy at the end of the guideI. The wave guide 3 is: similarly terminated' at' both offitsend's-"bymeans 33" and 35, and'theright hand end? oiithewave guide 5"i`s likewiseterminatedl by a body 37.

Theflefthand end of the guide 5 is' provided with a flange 39 or'similarmeans for coupling to an input' device such as another wave guide; notshown. A` vacuum tight seal or window 411- is provided in the guide 5?nearthe-.l'ei:`t hand? end'i The right hand end of the guide l" is"similarlyA provided with a window 43 and a flange 45 for cou-v pling to:a. load orother" utilization: devicel not shown..

1n the operation oi the device of Fig. l, the cathode assembly I3 ismaintained, by means of a battery or other source, not shown, at arelatively highly negative potential with respect to the wave guides andthe conductive envelope 1,

which may be grounded. The collector electrode 2'! may be at the samepotential as the wave guides, or may be maintained somewhat positivewith respect thereto by suitable connection to the external power supplysource.

The heater` I9 is energized by an external source connected between thepost 2| and one of the posts I5, causing the strip-like emitting surfaceof the cathode to produce a stream of electrons. The electric fieldbetween the cathode assembly and the slotted plate 23 accelerates theelectrons and directs the stream in the form of a relatively thin sheetflowing through the slots 25, Il", 9, Il', 9', Il and 9 in succession.

Wave energy to be ampliedris applied to the left hand end of the waveguide 5, inducing therein a travelling wave which runs down the lengthof the guide and is substantially totally absorbed by the terminatingmeans 31. The electrons issuing from the slot 25 travel at substantiallyequal velocities, and all enter the slot il at approximately the samevelocity. The wave travelling along the guide produces a high frequencyelectric field between the upper and lower slotted walls, the phase ofthe field being progressively retarded in the direction of propagation,i. e. from left to right in Fig. l. In passing through the eld in theguide 5, the electrons are velocity modulated, each linear element ofthe sheet-like stream being alternately accelerated and deceleratedaccording to the instantaneous variations in the eld through which ittravels.

The space between the guides 5 and 3 is substantially field-free, likethe drift space in a conventional klystron tube. In crossing this space,electrons which have been accelerated in the guide 5 tend to overtakeslower moving, earlier emitted electrons, and electrons which have beendecelerated are in turn overtaken by faster moving, later emittedelectrons. Thus each velocity modulated linear element of the streamforms into bunches wherein the electron density is higher than theaverage density of the stream, separated by spaces in which the electrondensity is less than the average.

Successive bunches enter the slot Il in the wave guide 3 at intervalsequal to the period rof the wave energy supplied to the wave guide 5,and in crossing the guide 3 they induce an alternating high frequencyeld between the upper and lower slotted walls. This field produces wavestravelling to the left and right respectively in the guide 3. The linearstream elements are hunched in progressively retarded phase down thelength of the tube from left to right, and thus the field induced at anypoint in the guide 3 is in phase with the field of the wave travellingto the right, and reinforces said wave. The waves travelling Vto theleft do not add in phase, and tend to cancel each other. This phenomenonis substantially the same as that occurring in the operation of thelong-slot type of directional coupler. The tapered end portions 2B and20' of the slots improve the directionality. Any remnant of left- Wardtravelling wave energy is absorbed at the fft end of the guide 3 by theterminating means The total high frequency field appearing across anelemental transverse section of the guide 3 is the sum of the fieldproduced by the bunched element of the electron stream which goesthrough that section, plus the field produced by the wave which arrivesat that section from the left. Thus, throughout a substantial portion ofthe length of the guide 3, the field is morefintense than the eld acrossthe corresponding portion of the guide E.

In passing through the more intense field in the guide 3, the electronstream is velocity modulated further, in the same manner as it wasvelocity modulated by the field in the guide 5. The resultant bunchingwhich occurs in the drift space between the guides 3 and l is morecornplete, and thus still more intense fields are induced in the waveguide I. The fields produced by successive elements of the electronstream add up in phase from left to right, as in the intermediate guide3, and produce a rightward travelling ampliiied wave which goes out theright end of the guide l i for utilization.

Referring to Fig. 6, the wave guides I', 3 and 5 may be curved intonearly complete circular form, instead of being rectilinear. The cathodeI3 is similarly curved. The vacuum envelope and collector electrode arenot shown in Fig. 6, but it will be apparent that they also may be madecircular or annular to conform with the wave guides. The output waveguide I' is terminated at its end 5l by low reflection means such asthose used in the tube of Fig. 1. The other end 53 of the guide I mayinclude a vacuum tight window or seal, and is adapted to be coupled to aload or utilization device.

The end 55 of the intermediate wave guide 3 is terminated like the end5I of the guide I. The other end 5'! of the guide 3' is coupled througha wave guide section 59 to the end 5l of the wave guide 5. The other end63 of the guide 5', which corresponds in position to the ends 53 and 51of the guides l and 3' respectively, is terminated by a low-reflectionplug like the ends 5l and 55.

Any signals appearing in the intermediate guide 3 will set up wavestravelling therein in the direction of the arrows 65. These waves arefed back to the guide 5' by way of the coupling section 55, and willcause velocity modulation of the electron streamfrom the cathode I3'.The stream will become bunched in travelling from the guide 5' to theguide 3', exciting further waves in the guide 3. Waves whose length areproperly related to the length of the feedback path 59 will excite theguides 5 and 3' in such phase that the electron bunches crossing theguide 3' will reinforce them, thus sustaining the oscillations. Thefrequency of oscillation may be varied within wide limits by varying thelength of the feedback guide 59, either electrically as by means of aphase shifter device, or physically as by a so-called trombonearrangement. The electron stream emerging from the intermediate guide 3'is velocity modulated so as to form relatively intense bunches at theoutput guide I. The Wave induced in the guide I travels in the directionof the arrow 51 tothe output end 53.

rI'he device of Fig. 6 has the advantages characteristic of that of Fig.1, i. e. high power capability and freedom from critical beam focussingproblems, and in addition offers convenient means for generating highfrequency energy without the limitations imposed by cavity resonatorssuch as are used in conventional klystron tubes.

Fig. 7 shows a cascade amplifier embodying the principles of the presentinvention, and comprising a single wave guide 1I formed helically withits turns overlying each other between an an-v Vnula'r cathode 12 and acollector electrode 19.

An annular accelerating electrode 11 is provided near the cathode 12,and a vacuum envelope 15 surrounds the structure. The guide 1l may besupported between the envelope 15 and a central cylindrical member 14.The ends 13 and 18 of the guide 1I are brought out through the envelope15 and provided with suitable seals or windows, not shown. I

In the operation of the tube of Fig. '1, energy to be amplified isapplied to the end 13 of the guide 1l, producing a wave which travelsdown the guide to the output end 18. In traversing the first turn of thehelix, this wave causes velocity modulation of the tubular electronstream, which arrives in partially bunched condition at the second turn.Providing the frequency of the input energy is properly related to thelength of one turn of the helix, the hunched stream will reinforce thewave, and produce further bunching at the next turn. This processcontinues with successive turns of the helix, the stream becoming moreintensely hunched with each passage across the guide. The amplified waveappears at the end 18 of the guide, which may be coupled to any suitableutilization means.

Figs. 8 and 9 show a further modification of the device of Fig. 7,wherein the progression of the wave guide down the structure is made insteps rather than as a uniform circular helix. The guide comprisesstraight sections 92, 92', 92 and 92' interconnected serially at theirends by arcuate guide sections 95, 95' and 95 at one end and 96, 96' and96 at the other.

The cathode consists of two straight strips 94 and 94' in line with thestraight wave guide sections on opposite sides of the central support|00, and the collector similarly comprises a straight strip 99 and acorresponding strip, not shown, on the other side of the support |00.vThe end 9| of the wave guide is adapted to be coupled to an inputdevice, and output is taken from the other end 93.

The operation of the tube of Fig. 8 is substantially the same as that ofFig. '7. As in the device of Fig. '1, the length of one turn about thestructure must be related to an integral number of wavelengths of theoperating frequency for optimum efficiency.

Since many changes could be made in the above construction and manyapparently widely diierent embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. An electron discharge device including a wave guide having twoopposed walls with electron permeable portions extending along thedirection of energy propagation in said guide, a cathode extendinggenerally parallel to said guide and adjacent one of said electronpermeable wall portions, a second wave guide similar to said first guideand disposed on the other side thereof from said cathode, said secondguide being substantially parallel to said rst guide and separatedtherefrom by a drift space, low reflection means terminating both endsof said second guide, a third wave guide similar to said rst wave guideand disposed on the other side of said second guide from said rst guideand separated from said second guide by a second drift space; means forsupplying high frequency energy to one end of said rst wave guide, lowreflection means terminating the corresponding end of'said third guide,and means for absorbing high frequency energy from the opposite end ofsaid third guide.

2. A cascade amplier device for high frequency wave energy, includingfirst, second and third electron permeable wave guide portions spacedapart transversely to the direction of wave propagation therein, meansfor producing and directing a sheet-like stream of electrons across saidrst, second, and third wave guide portions consecutively, means forsupplying high frequency energy to one end of said first wave guide,low-reflection terminating means at the other end of said rst waveguide, low-reflection terminating means at each end of said second guideand at the end of said third guide which is nearer the nrst mentionedend of said first guide, and means for leading high frequency energyaway from the other end of Isaid third guide.

3. An electronic device including a wave transmission conduit ofreentrant cross section transversely of the direction of wavetransmission, a slot in the face of the reentrant portion, said slothaving tapered ends, said slot extending longitudinally in saidreentrant portion, and means for providing a stream of electrons passingthrough said slot.

4. A cascade amplifier device for high frequency wave energy, includingan input wave guide, an intermediate wave guide and an output waveguide, each of said guides being of reentrant cross section transverselyof the direction of wave transmission therein and having two opposedlongitudinally extending electron permeable walls separated by adistance that is short compared to the major cross sectional dimensionof the guide, said guides being substantially longitudinally coextensivebut spaced apart from each other in the same direction as the spacingbetween said electron permeable walls, means for producing a thin sheetelectron stream having a Width substantially equal to the length of saidelectron permeable walls, and for directing said v stream through saidwalls and across said input, intermediate, and output guides insuccession. means for supplying high frequency energy to be amplied toone end of said input guide, low reection means terminating the otherend of said input guide, means for leading amplied energy away from theend of said output guide remote from the rst mentioned end of said inputguide, low reflection means terminating the other end of said outputguide, and low reection means terminating both ends of said intermediateguide.

ROBERT L. WATHEN.

lReferences cited in the me of this patent UNITED STATES PATENTS NumberName Date 2,122,538 Potter July 5, 1938 2,272,165 Varian et al. Feb. 3,1942 2,289,846 Litton July 14, 1942 2,320,860 Fremlin June 1, 19432,367,295 Llewellyn Jan. 16, 1945 2,368,031 Llewellyn Jan. 23, 19452,457,524 Bowen Dec. 28, 1948 2,485,661 Roach Oct. 25, 1949 2,509,374Sunstein May 30, 1950

